This invention relates generally to wireless communication systems. In particular, it relates to the automatic muting and wireless remote control of re-transmitted downlink radio frequency (RF) signals in a wireless system repeater. More particularly, this invention relates to automatic muting and wireless remote control of re-transmitted downlink radio frequency (RF) signals in a translating wireless system repeater
A cellular communication network provides its subscribers a method of communication in a given geographic area. The cellular communication network has certain advantages over a conventional phone system including increased service capability, better service performance, and efficient frequency spectrum utilization.
FIG. 9 illustrates a typical cellular communication network.
A typical cellular communication network 900 can be thought of as a hierarchical network. A subscriber typically carries a mobile unit 902a such as a cellular phone. The mobile unit 902a provides the user access to the cellular communication network 900. In order to gain access to the cellular communication network 900, the mobile unit 902a interfaces with a base transceiver station (BTS) 904a. 
The BTS 904a provides coverage for multiple subscribers in a specific geographic area, called a cell. As the mobile unit 902a enters the cell, the BTS 904a and the mobile unit 902a communicate with one another. Information from this initial communication is used by the cellular communication network 900 so that it can route calls to and from the mobile unit 902a. 
The BTS 904a has a limited coverage area. As a result, one technique for providing coverage for a large geographic area is to install multiple BTS units. In order to control and coordinate the multiple BTS units exemplified by 904a, 904b, they are interfaced with a base station controller (BSC) 906. The BSC 906 controls the wire and radio link between the BTS 904a, 904b and a Mobile Switching Center (MSC) 908.
The MSC 908 performs call processing functions such as transcoding and soft-hand-off. Since the MSC 908 has a location register, it also provides the location information necessary to track the location of the subscriber""s mobile unit 902a throughout the cellular communication network 900. The MSC 908 also provides an interface to an external network. The external network is typically a landline phone network such as the public switched telephone network (PSTN) or integrated services digital network (ISDN).
Because cellular communication is based on electromagnetic wave propagation, there is a problem with propagation loss. As electromagnetic waves propagate, the strength or power of the signal decreases rapidly as a function of the distance the electromagnetic waves travel from their source. As a result, when subscribers move to the edge of a cell of a BTS, their calls are sometimes unclear due to weak signals, or they are dropped completely. To help alleviate this problem, providers of cellular communications networks have come up with several solutions.
One method of providing improved signal strength is to install additional BTSs. A higher density of BTS installations will insure that the subscriber is always relatively close to a BTS, which in turn insures adequate signal strength. However, a major drawback to this solution is the high cost of a BTS.
Another solution is to use repeaters, which are considerably lower cost than a BTS, within the cellular communication network. Generally, repeaters receive a downlink signal from a BTS and re-transmit the downlink signal to a mobile unit after the downlink signal has been amplified by a downlink amplifier in the repeater. The process works similarly in reverse, where the repeater will amplify an uplink signal from the subscriber to the BTS with an uplink amplifier. The amplifiers provide an increase in signal strength which improves the clarity of the calls and prevents dropped calls. To distinguish the direction of the signals transmitted and received by the repeaters, the path between the repeater and the BTS is referred to as the xe2x80x9cbackhaulxe2x80x9d signal path.
As attractive as the use of repeaters are, they have a drawback. A repeater located remotely from its host BTS often has a fixed gain in both the downlink path (signal traveling from the BTS to the repeater) and uplink path (signal traveling from the repeater to the BTS). The amount of gain for each path is designed to compensate for the propagation loss suffered by the signals as they travel the fixed distance between the BTS and the repeater. The amount of fixed gain for each path is normally set at the time of installation and is not adjusted again. In the downlink path, the gain is most commonly based on the predictably weak signal power of the backhaul downlink signal received from the BTS. The amount of fixed gain is designed to amplify that incoming downlink backhaul signal to the maximum allowable downlink retransmit power of the repeater. The fixed gain creates a problem when an incoming signal with an unexpectedly high signal strength gets amplified, creating too high of an output level for the amplifiers, and a destructive phenomenon called saturation occurs. Operating an amplifier in saturation can damage the amplifier.
In order to protect the repeater""s amplifier, some repeaters have a power limiting circuit that is designed to prevent the output level from becoming too strong and saturating or damaging the repeater""s amplifiers. Another way to protect the amplifier is to use automatic level control (ALC) circuitry.
ALC is a technique which may be used in both the downlink and uplink paths of the repeater. In order to maintain optimum performance of the amplifier, it is desirable that the output of the amplifier perform within a certain range. The ALC assists in this function by sampling the input signal and if the input signal is within a specific range of input signal values, then the gain of the amplifier is not changed. However, if the input signal strength is above the upper limit of the input signal range, then the gain of the amplifier is reduced. If the input signal strength is below the lower limit of the input signal range, then the gain of the amplifier is increased. The sampling and comparison of the input signal strength can be performed by a processor such as a microprocessor or digital signal processor (DSP). The ALC can also be implemented by standard analog feedback techniques.
Although a repeater with ALC is an improvement over fixed gain repeaters, it is still not a complete solution. When ALC is used in a repeater downlink path, a problem arises when the downlink backhaul signal from the BTS is not present. The ALC responds to the missing downlink backhaul signal by measuring the input signal noise as a very low input signal level, and automatically adjusting itself to the maximum gain setting. While the downlink backhaul signal from the BTS is missing, the ALC may inadvertently amplify and re-transmit the input noise floor to a relatively high level which is undesirable. Furthermore, when the downlink backhaul signal to the repeater is restored, with the ALC gain at the maximum setting, the output amplifier can become very saturated and possibly be damaged.
To overcome the above stated problem, one solution has been to shut off the repeater""s output amplifier until the ALC had adjusted itself to the proper attenuation/gain setting. This output enable-and-disable function could be performed in response to commands received via a telephone line and modem, but this requires additional hardware, a phone line installation charge, and monthly billing expenses.
It is an object of this invention to provide a wireless system architecture whereby high efficiency broadband transceiver systems can be deployed at an initial build-out stage of the system in a cost-efficient manner.
A second object of the invention is to provide for automatic level control in a wireless system repeater while preventing saturation of output amplifiers in a wireless system repeater.
Another object of the invention is to provide protection against saturation of output amplifiers in a wireless system repeater with minimum hardware installation.
It is a further object of the present invention to provide all of the above-described advantages in a wireless system repeater translator.
Briefly, the invention features automatic RF muting and wireless remote control of the re-transmitted downlink RF signal in a wireless system repeater, in order to achieve the objects of the invention listed above. The ALC is controlled to set the initial gain at a safe setting and the output RF amplifier is disabled at initial startup until it receives a remote wireless enable signal. Accordingly, the requirements of a modem and a dedicated telephone line to the site, as well as the corresponding installation and monthly costs associated with that modem and phone line are eliminated.
This invention allows the ALC to be initialized at a safe setting, i.e. at a setting where variations in input signal strength will not result in output amplifier saturation. Further, the invention permits the output RF amplifier to be disabled at startup until it receives a remote wireless enable signal. This provides safe operation of the expensive high power amplifier component of the repeater unit.